An attachment pylon is provided so as to constitute the connection interface between a jet engine and a wing of the aircraft. It makes it possible to transmit, to the structure of this aircraft, the forces generated by its associated jet engine, and also allows fuel, electrical systems, hydraulic systems and air to be routed between the engine and the aircraft.
In order to transmit the forces, the pylon comprises a rigid structure, also termed the primary structure, frequently of the box type, that is to say formed by assembling upper and lower spars which are connected to one another via the intermediary of transverse ribs, wherein lateral panels may also be provided.
On the other hand, the pylon is fitted with a mounting system interposed between the jet engine and the rigid structure of the pylon, this system comprising, overall, at least two engine attachments, generally at least one forward attachment and at least one rear attachment.
Moreover, the mounting system comprises a device for taking up the thrust forces generated by the jet engine. This device may for example take the form of two lateral struts which are connected on one hand to a rear portion of the fan casing of the jet engine, and on the other hand to a rear attachment which is attached to the central casing of the latter.
In the same way, the attachment pylon also comprises a second mounting system interposed between the rigid structure of this pylon and the wing of the aircraft, wherein this second system, also called the attachment structure for attaching the pylon to the wing, usually comprises two or three attachments.
Finally, the pylon is provided with a rear secondary structure which separates and holds the systems while supporting aerodynamic fairings.
The rear secondary structure may in particular permit the installation of part of the hydraulic systems, and in particular the installation of components for hydraulic power generation. Thus, numerous hydraulic ducts may be located within this region of the attachment pylon which, this region being very narrow, requires the provision of straight ducts.
Moreover, these components for hydraulic power generation are also secured to the lower surface of the wing associated with the attachment pylon.
This placement in the rear secondary structure and this principle for attachment on the wing of the components for hydraulic power generation merit providing providing “flexibility” to the components for hydraulic power generation, so as to be able in particular to absorb the assembly tolerances and the relative movement, during flight, between the wing and the attachment pylon, that is to say more precisely the difference in thermal expansion since, during flight, the surface of the wing and the fuel therein are cold whereas the attachment pylon of the jet engine and the hydraulic ducts therein are at a higher temperature.
To that end, it is known to use sliding union connectors, and in particular low-pressure sliding union connectors, installed in line on the hydraulic ducts of the attachment pylon, and in particular on the hydraulic fluid aspiration duct located in the rear secondary structure. Such sliding union connectors thus aim to provide the ducts with the desired flexibility such that it is possible to compensate for the variations in movement between the wing and the rear secondary structure.
FIG. 1 represents, schematically and partially, in perspective, an example of an attachment pylon 20 for a jet engine of an aircraft. As this type of attachment pylon 20 is well known to a person skilled in the art, only a partial description thereof is given.
The attachment pylon 20 thus comprises a rear secondary structure 21 accommodating part of the hydraulic systems of the pylon 20, and in particular components for hydraulic power generation 22. In particular, a hydraulic fluid aspiration duct 11, of straight overall architecture so as to fit the space available in the rear secondary structure 21, is located inside this rear secondary structure 21.
FIG. 2 is an enlarged view of region A of FIG. 1. This FIG. 2 shows that the aspiration duct 11 extends between a first attachment point P1 and a second attachment point P2, which are both fixed relative to the structure of the wing. Moreover, at the second attachment point P2 there is located a fire shut-off valve 13, in particular a low-pressure fire shut-off valve 13 which, in an open position, allows the hydraulic fluid to circulate in the aspiration duct 11 and, in a closed position, prevents the hydraulic fluid from circulating in the aspiration duct 11.
In order to be able to compensate for the variations in movement between the wing and the rear secondary structure 21 of the attachment pylon 20, which may appear most particularly as a consequence of thermal expansion, there is provided a sliding union connector 12 mounted in line on the aspiration duct 11. The sliding allowed thereby may provide the desired flexibility for the aspiration duct 11.
Nonetheless, this solution which depends on the use of sliding union connectors is not entirely satisfactory.
Indeed, sliding union connectors may originate large leaks of hydraulic fluid, which are not permissible. Such leaks may then lead to repeated maintenance work to replace the sliding union connectors. However, replacing a sliding union connector requires very specific technical skills and is also time-consuming.